The invention relates to a clamping device for aligning and clamping two pipe ends with clamping plates which are arranged axially distanced, with clamping wedges extending in axial direction and which on a first side in radial direction are movably mounted on the clamping plates, and on a second side have a contact surface for acting on the pipe ends, with a guide for guiding the clamping wedges on the clamping plates and with an actuation means for moving the clamping wedges. The invention extends further to a clamping device set with several sets of exchangeable clamping wedges which have differing distances from the inner to the outer side.
For welding tubes it is necessary for the bordering ends of the tubes to be welded to be aligned to one another in a certain manner and held in this position. An ovality of the tubes which is often present would at the same time be alleviated as much as possible. In order to simplify the alignment and firm holding of the pipe ends in the desired position, there are basically two possibilities. The one possibility is to use clamping devices which on the inside or outside are attached to the pipe ends to be welded and which may be rigidly clamped to the ends of the tubes by moved clamping elements. Various embodiments of such clamping devices are known, which either in each case clamp only one pipe end so that two clamping devices are required, or which clamp both pipe ends.
The second, more oftenly used possibility is to hold the pipe ends after alignment in the desired position not by a special clamping device but by binding the two pipe ends to one another by a certain number of welding points and thus by fixing their mutual alignment. This possibility which is largely carried out by hand is above all applied when the ends of the pipe are to be welded to one another with a particularly high accuracy, and this is further effected under unfavourable conditions, such as in the offshore field. The disadvantage of this is that the quality fluctuates greatly. Often one achieves only very poor welding results. Clamping tools with clamping plates and clamping wedges are furthermore also known from the field of metal machining. Such clamping tools are for example used with milling for machining tubes. The miller is anchored in the pipe by way of the clamping tool inserted at one end of the tube. Similar clamping tools are also known with lathes. Common to all these is the fact that they are only designed for clamping one pipe end, and not for clamping and mutual alignment of two pipe ends, as is required when welding two pipe ends.
The disadvantage of the known clamping devices is the fact that the known clamping devices do not permit the achievement of the demanded accuracy. The manual alignment and clamping of the pipe ends by way of weld-binding is time consuming and expensive, in particular given poor environmental conditions.
It is therefore the object of the invention to provide a clamping device of the initially mentioned type, which permits a more simple and accurate clamping of two pipe ends.
The solution according to the invention lies in a welding device with the features of claim 1 as well as a clamping device set with the features of claim 15. Advantageous further formations are specified in the dependent claims.
Firstly some used terms are to be explained once:
A clamping device is to be understood as a device which serves for mutually aligning and holding two pipe ends in position with or without associated fittings or shape parts. As a rule the device at the same time is designed to align the pipe ends coaxially; however also other alignment types are conceivable, e.g. at a certain angular displacement to the respective middle axis of the two tubes.
Clamping plates are to be understood essentially as disk-shaped or annular elements which serve for mounting and for guiding the clamping wedges. With a clamping device which is designed for clamping on the pipe inner surface, the clamping plates are designed such that they may be introduced into the pipe ends; with a clamping device which is designed for clamping on a pipe outer surface, the clamping plates are designed such that they may be pushed over the pipe ends. The clamping plates although having usually a round shape, may also have a shaping which is dependent on the shape of the pipe ends which are to be welded to one another. Thus for example with clamping devices for welding square tubes it may be designed rectangular or square.
Elastic holding means is to be understood as a means which comprises at least one elastic element which may exert forces onto another component. With the elastic element it may be the case of such an element which obtains its elasticity essentially from its shaping, for example a spiral spring, or which obtains its elasticity from its material properties, such as for example rubber.
According to the invention with a clamping device of the initially mentioned type it is also envisaged to provide the guide with an elastic holding means for holding the clamping wedges on the clamping plates. By way of the elastic holding means it is achieved that with the clamping device according to the invention the pipe ends to be welded to one another may also be clamped with the required accuracy and security when the clamping device is not exactly aligned on the pipe ends but assumes an incorrect position, for example is arranged slightly tilted. The elastic holding element gives the clamping wedges within the guide a certain movability with respect to the clamping plates, so that the clamping wedges inspite of the incorrect position of the clamping device bear securely on the pipe ends and then finally allows these to be aligned and clamped. Thanks to it elasticity, although the holding means attempts to keep the clamping wedges in their normal position with respect to the clamping plates, it however when appropriate allows the clamping wedges to assume a position deviating from the normal position in order thus to compensate errors which result from a tilted arrangement of the clamping device in the pipe ends or resulting from other inaccuracies. A further advantage of the elastic holding means according to the invention is the fact that it has a loss-preventing effect. The loss-preventing effect is based on the fact that the elastic holding means attempts to hold the clamping wedges in their normal position to the clamping plates. It therefore counteracts undesired movements of the clamping wedges with respect to the clamping plates and thus holds the clamping wedges on the clamping plates.
It is surprising that on the one hand with the elastic holding means according to the invention the clamping wedges may be given a certain degree of freedom with respect to the clamping plates for compensating alignment errors, such as for example tiltings, without worsening the security and accuracy of the guiding of the clamping wedges on the clamping plates.
Preferably the elastic holding means comprises a spring-loaded ball, which is arranged on one of the two, the clamping plate or the clamping wedges in order to cooperate with the other of the two, the clamping wedges or the clamping plate. The ball impinged by a spring with force exerts a holding force by way of which the clamping wedge is held on the clamping plates. This force is usefully dimensioned such that on the one hand it is sufficiently high to hold the clamping wedges on the clamping plates, but on the other hand with the occurrence of greater forces, as occur when clamping the clamping device in the tilted position, is overcome and thus permits a movement of the clamping wedges out of their normal position.
Often it is the case that the spring-loaded ball is arranged on the clamping plates and acts on a surface of the clamping wedge; one may however also reversely envisage for the spring-loaded ball to be arranged on the clamping wedges and to act on the surface of the clamping plate.
Usefully the elastic holding means comprises a deepening which is arranged on the one of the two, the clamping wedges or the clamping plate, and which cooperates with the spring-loaded ball. The deepening together with the spring-loaded ball forms a positive fit which permits a more secure holding of the clamping wedges on the clamping plates than with friction forces on their own. Furthermore by way of the shape of the deepening one may set a movement path for the guiding of the clamping wedges on the clamping plates. It is particularly advantageous to design the deepening as a channel. The clamping wedges may then be led along this movement path (normal position) without a significant counterforce by the elastic holding means.
Usefully a hollow bolt is provided as a bearing for the spring-loaded ball. The hollow bolt permits a particularly simple mounting of the ball as well as of the spring impinging the ball with force. Furthermore the hollow bolt permits a simple adjustment of the bias of the spring and thus of the holding force of the spring-loaded ball.
Preferably the guide is designed on the manner of guide grooves, whose groove base forms an oblique surface. Grooves permit a particularly simple and useful manner of guiding the clamping wedges on the clamping plates. The oblique surface which usefully cooperates with a counter oblique surface on the guided element, as a rule clamping wedges, determines the relation of the movement between the clamping plates and the clamping wedges. By way of changing the axial distance of the clamping plates the oblique surface permits the movement of the clamping wedges in the radial direction. Its angle determines the ratio of these two movements and the force transmission ratio between the force which must be mustered for moving the clamping plates towards one another or away from one another, and the spreading force of the wedge plates.
Usefully in the region of the guide grooves there is provided a tangential bore for accommodating the spring-biased ball, which with its one end ends in the guide groove and with its other end on the circumferential surface of the clamping plates. With such a tangential bore there is formed a particularly space-saving and simply manufacturable receiver for the spring biased ball and where appropriate the hollow bolt. By changing the position of the hollow bolt in the bore, for example by rotation, in a simple manner a change in the spring bias and thus of the holding force exerted by the ball may be carried out.
Preferably the clamping wedges consist of a copper-chrome-nickel alloy. This alloy has favorable friction properties so that no lubrication between the clamping plates and the clamping wedges is required. By way of this the construction of the clamping device is simplified considerably, also in operation there result considerable simplifications on account of this. They may however also consists of other materials, in particular stainless steel, titanium, bronze and alloys.
Usefully on the outer end faces of the clamping plates there are arranged sealing means which are designed for the sealing cooperation with surfaces of the pipe ends. By way of these sealing means the space located between them with the clamping device is separated off from the remaining inside of the pipe in a gas-tight manner. By way of this one prevents the access of damaging gases, for example atmospheric oxygen, from the inside of the pipe to the welding location between the pipe ends. By way of this one may achieve a better welding result.
Preferably there is provided a forming gas conduit on at least one of the clamping plates in order to conduct supplied forming gas into the region between the clamping plates. The forming gas serves for the further improvement of the surrounding conditions at the welding location, in particular for creating a protective gas atmosphere. The forming gas conduits integrated into the clamping plates permit a particularly simple, reliable and low-loss supply of forming gas.
Usefully there is provided a connection plate with a connection and with a passage opening for the forming gas to be supplied, which via an annular channel is in connection with the forming gas conduit of the clamping plate. With the separate connection plate a particularly simple and universal connection for the forming gas is possible. Thanks to the annular channel the connection plate may lie at any angular position with regard to the clamping plate so that it becomes possible to rotate the connection plate with respect to the clamping plate also in operation of the clamping device. Furthermore the annular channel has the advantage that with only one connection on the connection plate one may supply a plurality of forming gas conduits in the clamping plate, inasmuch as the forming gas conduits are arranged on a circular path.
Usefully there is provided at least one bleed opening on one of the clamping plates, preferably on the one without a forming gas guide. By way of the bleeding opening excess forming gas may be led away out of the space between the two sealing means. By way of this it is avoided that an undesirable excess pressure arises in the space between the sealing means and thus at the welding location on account of the supplied forming gas.
Usefully the actuation means is designed for moving the clamping edges. Alternatively they may also be designed hydraulically. The actuation means does not need to act directly on the clamping wedges. With a tried and trusted embodiment form it rather acts on the clamping plate whose movement is then transmitted onto the clamping wedges via the guide.
According to a particularly preferred embodiment form of the invention which where appropriate is also to enjoy independent protection, one provides a spreader ring consisting of at least two segments whose outer circumferential surface comprises a peripheral pressure saddle. In such a spreader ring the pipe surface in the region in which the welding seam is to be attached may be pressed in slightly in order thus to widen the pipe in the region of the later welding seam. The widening of the pipe in this region has the advantage that the full width of the pipe may also be maintained when the pipe contracts after the competed welding, in particular in the region of the welding seam. Without any previously carried out widening it may occur that then in this region the width of the pipe is restricted; if however a widening of the pipe in this region has been carried out with the spreader ring, then the pipe also after welding has the full width in the region of the welding seam. A further surprising advantage of the widening lies in the fact that by way of this it is indeed in the critical region of the welding location that a possible ovality of the pipe ends may be prevented. At the same time the widening may be relatively slight, according to pipe thickness an amount of 0.1-0.4 mm is completely sufficient. However one may also widen by a greater amount, one may even achieve up to 1.5 mm with a mechanical actuation means without difficulty. The spreader ring may be designed such that it may either be placed on the clamping wedges, or when the clamping wedges are omitted, it may be assembled directly between the clamping plates, which then only have a small distance to one another. By way of activating the actuation means the clamping plates move towards one another, by which means the segments of the spreader ring, indirectly via the clamping wedges or directly in the radial direction, is forced against the pipe surface in order to widen this. This widening is only required in the direct vicinity of the welding location in order to keep the forces required for the widening small, the pressure saddle only has a relatively slight extension of a few mm, preferably about 4-8 mm in the axial direction.
Usefully the spreader ring on its inner circumferential surface comprises bevellings. With these bevellings it is possible for the spreader ring to be arranged directly between the clamping plates and for these to directly cooperate with the spreader ring, that is to say without the clamping wedges arranged therebetween. Usefully, the clamping plates, on their edge envisaged in each case to cooperate with the clamping wedges, comprise a chamfer whose angle preferably corresponds to the bevelling. By way of this chamfer a particularly good bearing of the clamping plate on the spreader ring is achieved. The chamfer at the same time extends over a smaller region than the depth of the slot accommodating the clamping wedges so that between the slots there remains sufficient material in the clamping plate for the secure guiding of the clamping wedges. By way of the bevelling on the inner circumferential surface of the spreader ring and the chamfer on the clamping plate at the same angle, in an advantageous manner it is achieved that the clamping plates with the spreader ring form an independent system which is independent of the clamping wedges. Thus the angle of the bevelling or chamfer may be selected independently of the angle of the oblique surface in the guide groove so that there results a different force transmission ratio between the force of the actuation means acting axially on the clamping device and the radially acting pressing force resulting therefrom on the one hand and the clamping force on the other hand. Preferably the angle of the bevelling or chamfer is smaller than that of the oblique surface of the guide grooves so that one achieves a force transmission ratio which is as high as possible. This has the advantage that with an unchanged actuation means one may achieve high spreading forces in order thus also to be able to widen tubes with a relatively large wall thickness.
The invention further relates to a clamping device set for aligning and clamping pipe ends in various sizes, with clamping plates which are arranged axially distanced, with clamping wedges which extend in the axial direction and which on a first side are movably mounted on the clamping plates in the radial direction and on a second side have a contact surface for acting on the pipe ends, with a guide for guiding the clamping wedges and with an actuation means for moving the clamping wedges, characterized in that the guide is provided with an elastic holding means for holding the clamping wedges on the clamping plates, wherein the clamping wedges are exchangeable and several sets of clamping wedges are provided which have different distances from the inner to the outer side. Furthermore they may consist of different material.
By way of the fact that the clamping wedges are exchangeable, and several sets of clamping wedges are present which differ in their dimensions, an adaptation of the clamping device to the respective dimensions of the pipe ends to be welded to one another may be carried out. If two pipe ends with a small diameter are to be welded to one another, then from the sets of clamping wedges one may select and apply in the clamping device a set of clamping wedges which has a fitting small distance from the first side on the side of the clamping plate to the tube-side second side. If one is to weld a pair of pipe ends with a larger diameter to one another, then one selects and uses a set of clamping wedges which has correspondingly large dimensions. By way of this there results a greater range of application of the clamping device according to the invention with regard to the pipe sizes which may be welded. By way of a simple exchange of the set of clamping wedges an adaptation to different pipe diameters may be effected.
Usefully the clamping wedges are designed multi-piece with a sliding piece on the side of the clamping plates and an attachment piece on the side of the tube, wherein the attachment piece is exchangeable and there is provided a set of attachment pieces of different sizes. As has been shown, is not completely necessary to exchange the clamping wedges as a whole, but it may be sufficient to change the part of the clamping wedge which determines the distance of the edge on the side of the clamping plate to the tube-side edge. This has the advantage that on exchange the clamping wedges are not taken out of their guides on the clamping pates and the new one replaced therein. It is sufficient to place another attachment piece onto the sliding piece remaining in the guides on the clamping plates. Usefully there is provided a quick-closure for the connection of the attachment pieces on the sliding pieces.